Gnathia aff. maculosa Ota & Hirose, 2009

Ota, Yuzo, Erasmus, Anja, Grutter, Alexandra S. & Smit, Nico J., 2024, Two new species and new host and distribution records of Gnathia Leach, 1814 (Crustacea, Isopoda, Gnathiidae) from Western Australia and the Great Barrier Reef, Australia, ZooKeys 1193, pp. 125-144 : 125

Gnathia aff. maculosa Ota & Hirose, 2009

Figs 7A-D , 8

Gnathia maculosa Ota & Hirose, 2009a: 50, 51, 56, 57, figs 1-3, 5.

Type locality.

Nakagusku Bay (26°N, 127°E), Okinawajima Island, Japan.

Material examined.

Australia • 1♂ (5.0 mm TL, 4.5 mm BL, SEM); reared from a juvenile collected from a cowtail stingray Pastinachus sephen ( Forsskål, 1775) (TL and sex, unknown), Lizard Island , GBR (14°40'08"S, 145°27'34"E), 19 June 1998, Ian D. Whittington leg. (QM W29821) . 1♂ (5.5 mm TL, 4.9 mm BL, dissected); reared from a juvenile collected from a species of Rhynchobatus (TL 126.5 cm, female), Shark Bay , Heron Island, GBR (23°26'37.03"S, 151°55'5.64"E), 7 Oct. 1998, Ian D. Whittington leg. (QM W29822) .

Remarks.

The male morphologies of these GBR specimens show the deep and narrow dorsal sulcus on the cephalosome, the narrow body (Fig. 7A, B ), and the almost semicircular pylopod article 1 with three areolae (Fig. 7C ). These characters can be identified as Gnathia maculosa Ota & Hirose, 2009. However, this species was originally described from the Ryukyu Islands, southwestern Japan ( Ota and Hirose 2009a) and our records are a great distance from this island group. The apices of the frontolateral processes on anterior margin of heads of the present specimens are smooth, while those of original description are serrate ( Ota and Hirose 2009a). The number of setae on the pleotelson of the present species is two pairs (Fig. 7D ), while that of the original description is three pairs ( Ota and Hirose 2009a). Thus, these GBR specimens are identified as G. aff. maculosa .

The GBR specimens of G. aff. maculosa have a bundle of several long setae on the ventral frontal border (Fig. 8 ). Ota and Hirose (2009a) did not show the ventral frontal border but the Japanese specimens G. maculosa also have a bundle of several long setae (YO pers. obs.).

Distribution.

Gnathia aff. maculosa : Lizard Island and Heron Island, Great Barrier Reef, Australia; Gnathia maculosa : Okinawa-jima Island, Kume-jima Island, Ishigaki-jima Island, Japan.

Habitat of adults.

Unknown.

Hosts.

Two elasmobranch species from GBR: Pastinachus sephen ( Forsskål, 1775), Rhynchobatus sp.

Hosts of G. maculosa .

Ota and Hirose (2009a) recorded the two host elasmobranchs of G. maculosa and Ota (2015: table 2) summarised gnathiids ectoparasitising on elasmobranchs in the Ryukyu Islands and documented G. maculosa obtained from 11 elasmobranch species including two host species previously recorded by Ota and Hirose (2009a): Rhynchobatus djiddensis ( Forsskål, 1775), Neotrygon orientalis Last, White & Séret, 2016 [ Neotrygon kuhlii Müller & Henle, 1841 in Ota 2015], Taeniura meyeni Müller & Henle, 1841, Himantura undulata (Bleeker, 1852), Himantura sp., Aetomylaeus vespertilio (Bleeker, 1852), Aetobatus ocellatus (Kuhl, 1823) [ Aetobatus narinari (Euphrasen, 1790) in Ota 2015], Rhinoptera javanica Müller & Henle, 1841, Nebrius ferrugineus (Lesson, 1831), Triaenodon obesus ( Rüppell, 1837), and Negaprion acutidens ( Rüppell, 1837).

Site of infection on host in G. maculosa .

Gill chambers, interbranchial septa, gill filaments, and the floor of oral cavities. Rarely nostrils, body surface near the gill slits, or claspers.

Figures

Figure 7. Gnathia aff. maculosa Ota and Hirose, 2009 (A-D; QM W 29822) and G. trimaculata Coetzee, Smit, Grutter & Davies, 2009 (E; QM W 29825) A whole body (dorsal view) B pereonite 1, cephalosome, and mandible (dorsal view) C pleotelson (dorsal view) D right pylopod (ventral view) E frontal border of G. trimaculata (dorsal view).

Figure 8. Scanning electron micrograph of the ventral view of the frontal border of Gnathia aff. maculosa Ota & Hirose, 2009 (QM W 29821) showing bundles of several long setae (two arrows). Scale bar: 500 µm.